The present invention in one aspect relates to seismic geophysical prospecting apparatus; and more particularly, it relates to apparatus for use therein to improve the quality of recorded seismic data by determining the conformity of an energy pulse emitted by an emission source to defined energy pulse characteristics.
The present invention relates in another aspect to electronic apparatus for analyzing the waveform shape of an electrical signal input thereto to determine its conformity with a defined waveform shape; and more particularly, it relates to electronic apparatus for so analyzing an electric signal that is representative of the energy pulse emitted from a seismic source.
In geophysical prospecting of the earth's strata by the creation of seismic waves, permitting seismic profiles to be obtained of a selected geological area, discrete energy pulses are emitted from an emission source to create mechanical waves in a stratum that are reflected back to seismometers.
Seismic prospecting of geological strata utilizes energy emission sources which are either of an explosive type disposed beneath the ground surface, or a source operating on the surface, such as a dropping weight. In weight drop seismic prospecting, several weight drop seismic sources are utilized in relation to a single line of geophones. The weight drop seismic sources are sequentially activated to transmit successive energy pulses into the strata at separated locations within the selected geographical area. Reflections of the wave produced by each energy pulse are received by a single line of geophones, with the reflected waves being transduced into representative electrical signals that are subsequently processed and recorded.
Since geophysical prospecting using weight drop seismic sources requires that the sources be spatially separated, it is typically the case that each of the weight drop seismic sources operates at a location having a topography that is at variance with the topography of the locations at which each of the other weight drop seismic sources operates. Therefore, the energy pulses transmitted into the strata by the seismic sources may be at variance with one another, and the resulting reflections will correspondingly exhibit dissimilar waveform characteristics. A variation between energy pulses emitted by separated weight drop seismic sources will be particularly likely to exist when prospecting operations are being carried out in geographical areas that exhibit a rough terrain, such that the area of contact between the ground and the dropped weight differs for each seismic source.
In order to improve the signal-to-noise ratio of seismic reflection data before velocity determination by computer processing, it has become common practice to sum several traces having the same source-to-geophone separation but different common depth points. This procedure is referred to as "vertical stacking".
Since vertical stacking entails the summation of all output traces from a particular geophone, the shape of the signals on all traces must be identical. Variations in the seismic source energy pulses that produce the trace data will reduce the quality of the stack due to the dissimilar characteristics of the reflections from drop to drop.
Therefore, particularly when multiple weight drop seismic sources are utilized in geophysical prospecting, it is necessary for a satisfactory vertical stacking procedure that the energy pulses transmitted by the sources be substantially identical, such that the reflections of each of the energy pulses will be of similar characteristics.